Four children were killed in a mobile home fire on Wednesday afternoon in Hartsville, S.C., authorities said.

The four children killed included twin girls, perished Wednesday afternoon when fire swept through the South Carolina mobile home. The 1-year-old twins and their brothers aged 3 and 4 were found dead in the home after firefighters put out the blaze, Darlington County Coroner Todd Hardee said.

Hardee said autopsies are planned Thursday as part of an investigation to determine the cause of death and their identities.

Sheriff Wayne Byrd said the mother was in the yard when firefighters arrived. He didn’t elaborate.

The fire is under investigation by both the sheriff ‘s department and the State Law Enforcement Division. No charges have been filed and authorities were preparing to talk with the mother.

Russell Cox, a spokesman for the city of Hartsville, said firefighters took about 10 minutes to put out the flames and then found the victims in the charred interior of the home, which was located on a street lined with mobile homes

Hartsville is a city of some 8,000 people about 60 miles east of the state capital, Columbia.

While a photograph tweeted by the Darlington County sheriff’s office showed the charred interior of the home, it indicated the outside appeared to be relatively undamaged. A tricycle and another children’s toy could be seen in the yard.

Smoke could be seen still wafting from an open front door where fire hoses snaked through the opening.